There is little magic in standard chokes. Choosing one that's equal in size and resistance is as close to perfection as one can get without an original part to test, and replicate. The schematic is a bit messy -- however, 50mA is more than sufficient as Martin has already lent his wise guidance on.
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1484 Hum
Moderators: pompeiisneaks, Colossal
Re: 1484 Hum
Mercury offers a 1484 replacement choke, which is also used in the 1485. The 1485 was the same amplifier, but with a second power amplifier added on to the chassis.
I think any reasonable replacement choke would do the job just fine. The choke feeds the screens and the preamp stages, off of the 3rd leg of the voltage quadrupler. Screen current would be the dominant factor, and it isn't all that high, especially at reduced voltage in this case.
https://www.hammfg.com/electronics/tran ... ke/153-159
You can shop at that link by dimensions and current/Henries.
The choke should be fairly high H (7H is a good bit of inductance) but doesn't need a high current rating.
Maybe double check that the 20uf@450v is wired in correctly. I'd think if the power supply was good, you wouldn't get any hum with the PI tube pulled out.
I think any reasonable replacement choke would do the job just fine. The choke feeds the screens and the preamp stages, off of the 3rd leg of the voltage quadrupler. Screen current would be the dominant factor, and it isn't all that high, especially at reduced voltage in this case.
https://www.hammfg.com/electronics/tran ... ke/153-159
You can shop at that link by dimensions and current/Henries.
The choke should be fairly high H (7H is a good bit of inductance) but doesn't need a high current rating.
Maybe double check that the 20uf@450v is wired in correctly. I'd think if the power supply was good, you wouldn't get any hum with the PI tube pulled out.
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Smokebreak3
- Posts: 59
- Joined: Wed Dec 28, 2022 12:45 am
Re: 1484 Hum
I went with the Hammond 156L, and it works perfectly in the amp. This was 100% the cause of the hum, as it hummed badly with a 20W (overkill I know) 150r resistor there.
Even with the PI tube pulled, the ripple would have passed right through the Cathodyne's Rp and through the coupling cap to the outputs. Apparently it wasn't enough to cause hum at the speakers when only reaching the screens(with grid couplers lifted) , but at the grids it was deadly
https://www.mouser.com/ProductDetail/546-156L
Even with the PI tube pulled, the ripple would have passed right through the Cathodyne's Rp and through the coupling cap to the outputs. Apparently it wasn't enough to cause hum at the speakers when only reaching the screens(with grid couplers lifted) , but at the grids it was deadly
https://www.mouser.com/ProductDetail/546-156L